VAX (Virtual Address eXtension) is an established line of mid-range server computers from the Digital Equipment Corporation (DEC). It followed DEC's PDP-11 in 1978 and also introduced a new operating system, VMS. VAX included a 32-bit processor and virtual memory. Historically, VAX has competed with a number of Hewlett-Packard and IBM computers in the small enterprise and university-scientific marketplace. In earlier times, this size and price range of computer was known as the minicomputer. Today, VAX and its competitors sell "servers" for business networks that use the client/server computing model.
DEC indicates that over 250,000 VAX systems are in use. As of October, 1996, models were in the $18,000 to 46,000 price range. Based on VMS, its operating system is called OpenVMS. Among other features, OpenVMS can be used with special software that facilitates its use with Windows NT servers. OpenVMS also supports the open standard Portable Operating System Interface set of commands and C language programming interface, effectively making it both a VMS system and a UNIX system.